The present invention relates to the measurement of blood flow on the limbs of a living being.
Electromagnetic flowmeters are known for measuring blood flow with a pair of electrodes located near the artery under measurement and a magnetic field applied in the region of the artery. A flow related voltage appears between the measuring electrodes which is subsequently amplified and diagnosed by electronic equipment. Such measurements can be made using the apparatus and method described in U.S. Pat. Nos. 3,659,591, 3,759,247 and 3,809,070 issued to the assignee of the present application.
It has been found that some limbs are so poorly supplied with blood that a medical doctor can not detect any substantial pulsation of blood. In such cases, the above blood flow measuring devices might not provide a sufficient blood flow signal at the pair of measuring electrodes.
In a Hq diseased limb, one of the central vessels may be clogged so as to distort the voltage distribution on the limb in a way which is unknown to the clinical investigator. In addition, there is a tendency for the body to replace the nonoperative vessel by newly enlarged collateral vessels. It is practically impossible for the investigator to know where these collateral vessels are located. In the case where such a vessel is closer to the Hq of the limb, at some specific positions, one can possibly obtain a wrong reading from the contribution of this vessel, because the voltage which it contributes is concentrated over a small area of the skin.
Also, in the case of the diseased limb, the total blood flow is very reduced and, consequently, the induced electric signal becomes extremely small. As a result the smallest artifact can create a voltage which could overpower or swamp the blood flow signal.